Sources and Health Risks of PM2.5-bound PAHs in a Small City along with the "Clean Heating" Policy

Levels, composition, and sources of PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) vary significantly along with the "Clean Heating" (CH) policy in Beijing-Tianjin-Hebei (BTH) region, whereas the PAH characteristics with CH in small cities still remain unclear. A field observation was conducted in Baoding City, a small city within the BTH region, in winter of 2019 covering both the pre-heating season (PHS) and the heating season (HS). From the PHS to the HS, the mean concentrations for both PM2.5 and Sigma(18)PAHs increased from 69.1 to 125.0 mu g m(-3) and from 8.09 to 26.2 ng m(-3) due to the heating activities. The far lower PAHs in this study than those of small cities before CH implementation indicated the CH effectiveness. Higher diagnostic ratios (DRs) of FA/(FA + PY), BaA/(BaA + CHR), and IP/(IP + BgP) in the HS were in agreement with the increased coal/biomass usage. Positive matrix factorization (PMF) demonstrated that biomass/natural-gas burning (BNGB) contributed most to PAHs of 36.9% in the HS, the increased natural gas (NG) usage for heating should be responsible for this contribution due to the policies of biomass-burning prohibition and "Coal to Gas". Coal combustion (CC) shares increased by 152% in the HS despite the "Coal Banning" project. Again, the medium-molecular-weight PAHs (MMW-PAHs) increased most by 400% in the HS, evidencing the increased impacts of fossil-fuel consumptions. As an indicator for carcinogenic risk, BaP increased from 0.937 in the PHS to 1.29 ng m(-3) in the HS. Furthermore, the incremental lifetime cancer risks (ILCR) and BaP equivalent concentrations (BaPeq) increased in the HS. The mean ILCR values of 1.15 x 10(-6) for adults in the HS exceeded the threshold of 1 x 10(-6), while they were lower than 1 x 10(-6) for children in both the PHS and the HS, and adults in the PHS due to the CH positive effects.